PROPOSAL (Adapted from the applicant's abstract): Characterized by intermittent airway closure during sleep, OSA is extremely prevalent, afflicting 2-4% of Americans. If left untreated, a large body of evidence convincingly shows that OSA can lead to daytime hypertension. In fact, 20-30% of patients with OSA will have hypertension, and 40% of patients with hypertension have occult OSA. The question then is how to identify patients who have OSA from among this high-risk population of individuals with hypertension. Polysomnography (PSG), the current diagnostic gold standard, is expensive and inconvenient. Several simple techniques to screen for OSA are available: questionnaires, craniofacial measurements, nocturnal oximetry and airflow monitoring devices. However, no one has compared their relative efficacies or costs in one unified population. The investigator proposes to compare these screening tools against full PSG's in a cohort of patients at high risk for OSA, i.e., outpatients with hypertension. Among the cases of OSA subsequently identified, the applicant next proposes to evaluate outcomes of treatment of OSA with continuous positive airway pressure (CPAP) in a randomized, placebo- controlled trial. The specific aims, therefore, are: 1) to compare the accuracy of several screening strategies for OSA in outpatients with hypertension; 2) to determine their relative economic costs; and 3) to determine the effect of CPAP therapy on blood pressure (BP) and sympathetic activity during sleep and awake states in OSA patients with hypertension. These projects are extraordinarily important. They have the potential to lead to dramatic changes in the approach to management of the patient with hypertension. Along with a complementary program of didactic training, they will constitute a strong foundation of experience for the applicant in her goal of becoming an independent clinical investigator.